The present invention relates to a classification instrument for classifying airfoil or vane elements such as turbine stator vanes and the like. More particularly, the invention relates to a classification instrument capable of classifying or determining both the blocked area and open flow area for the airfoil or vane elements.
A number of classification gauges have been developed in the past in order to provide an accurate determination of the relative effective open area in the various stages of turbojet engines and the like. Such classification gauges have been particularly directed toward the classification or determination of such values in connection with individual vane elements or vane clusters including a plurality of guide vanes, turbine blades and/or other similar structures. For example, U.S. Pat. No. 3,464,119 issued Sept. 2, 1969 to Elmer L. Griggs, past president of assignee, disclosed a precision classification gauge for classifying individual guide vanes or the like for turbojet engines in order to facilitate assembly of various stages of the engine according to predetermined values for the effective open areas of the individual vanes. U.S. Pat. No. 3,959,886, issued June 1, 1976 also to Elmer L. Griggs, disclosed a similar classification gauge adapted for classifying or determining the relative effective open area for vane clusters rather than individual vane elements. U.S. Pat. No. 4,024,646 issued May 24, 1977, also issued to Mr. Griggs, disclosed yet another apparatus for simultaneously gauging and aligning movable elements of guide vane assemblies including a plurality of vanes or airfoil elements in order to both classify and adjust the effective open area for the vane assembly.
Substantial background information is set forth by the above-noted patents, particularly the first noted patent and reference may be had to those patents for a more complete understanding of certain aspects of the present invention. Generally, it has been found important to obtain the precise classification or determination of the effective open area for individual guide vanes or for adjacent guide vanes in a cluster or assembly. This value is commonly referred to as "throat area" and must be precisely established for various stages in machinery such as turbojet engines in order to permit proper performance.
The classification gauges disclosed by the above-noted patents have been found to be particularly suitable for determining the proper classification of individual guide vanes, vane clusters and even complete arrays of vanes or similar structures. Generally, the above-noted classification gauges function to accurately position within a precision jig one portion of an airfoil, such as its trailing edge, other portions of the airfoil then being precisely measured in order to classify the effective open area for the individual vanes or vane assemblies. Very generally, the open area for such vanes or vane assemblies may be determined by accurately monitoring the location of the trailing edge for the vane as well as its convex airfoil surface and the effective length of the vane or vane assemblies.
However, it has been found that an even greater amount of information concerning the vane structure is necessary in order to completely assess or preclassify the vane for use in a vane cluster or assembly. Preferably, it is important to know both the blocked area provided by each vane as well as the open or flow area provided by the individual vane either alone (defined herein as "effective open area") or in combination with an adjacent vane structure (defined herein as "open flow area"). In this regard, the term "blocked area" is employed herein to refer to the effective thickness of the vane or airfoil element multiplied by the effective length of the vane. The length of the vane is of course determined by the spacing between the buttresses or flanges arranged at the end of each vane.
Similarly, the open flow area is established as the effective opening width between a pair of adjacent vanes multiplied by the effective length for the opening between the vanes. Here again, the length of the opening between the vanes is also determined by the spacing between the buttresses for the two adjacent vane elements. Finally, in connection with the open flow area, it may be seen that the arrangement of each vane upon its buttresses contributes to the open flow area between the two adjacent vanes. Thus, in order to accurately assess each individual vane element, it is necessary to know the effective open area provided by the individual vane regardless of the vane structure to which it will be adjacent in a given assembly. Given the information outlined above, more accurate classification of the individual vane elements is possible in order to even more accurately assess its contribution within a given vane assembly.
Further, it has been realized in connection with the present invention that the traditional values of such a vane element including the locations of its trailing edge, convex airfoil surface, etc., are important in determining the values for blocked and open flow area as discussed above. In addition, it has been determined that other factors including particularly airfoil rotation, airfoil displacement and airfoil twist may further affect these area values. In this regard, airfoil rotation refers to the angular relationship between the airfoil vane element and its respective buttresses or flanges. Rotation of the airfoil in either a clockwise or counterclockwise direction upon the supporting buttresses will result in modification for both the blocked and open flow area values. Similarly, airfoil displacement refers to the location of the airfoil or vane elements upon its respective buttresses. Airfoil displacement is particularly concerned with relative positioning of the airfoil or vane elements upon their respective buttresses in a direction perpendicular to the path of airflow past or through the individual vanes or vane assemblies. Finally, airfoil twist refers to relative rotation between opposite ends of the individual airfoil or vane elements. Relative rotation may arise for example during manufacturing of the vane element with buttresses formed at opposite ends of the vane or airfoil. More commonly, such relative rotation may be produced between the opposite ends of an individual vane element when its buttresses are secured in a vane assembly such as in a given stage of a turbojet engine. For example, if the base surface of the opposite buttresses are not precisely aligned, or if the surfaces to which the buttresses are attached are not properly aligned, twisting or relative rotation between the opposite ends of the vane element may be produced by the high temperatures and forces within the engine. Accordingly, the present invention contemplates consideration of the above factors in order to more precisely classify the individual vane elements.